In injection molding, upper and lower mold halves are brought together to define a mold cavity into which heated molten plastic is injected under pressure. The mold halves are typically vertically aligned with an upper mold portion termed the cavity half and a lower mold portion termed the core mold half. For forming holes or apertures or undercuts through sides or on other locations of molded pieces, side action coring elements are provided which are projected into the molding cavity as the mold halves are closed and which must be retracted from the cavity as the mold is opened and before ejection of the part can take place. In conventional molds, this is accomplished by using guide pins and/or offset cams fixed in the cavity half of the mold which cooperate with a slide carrier which carries the coring element and includes a bore machined at an angle therein. As the mold halves close and open, the angled pin is received for sliding in the angled bore of the carrier for causing the side action to slide laterally on wear plates attached in the core half.
One problem with current side-action devices is that the alignment of the angled pin with the carrier bore must be fairly exact to prevent damage or breakage of the relatively small angled pin. In addition, the closing and opening forces during cycling of the mold by the press are relatively large and create high forces between the engaging surfaces of the pin and bore which can produce scoring and galling of these surfaces. Such surface wear is also exacerbated by any misalignment problems. The sliding action between the coring element carrier and the wear plate/gib assembly can also produce galling of these surfaces generating high frictional resistance which the angled cam pin may not be able to overcome before it fails. Accordingly, there is a need for a side-action mechanism which does not utilize the angled cam pins and bores of the prior art and is more forgiving in terms of the tolerances required for trouble-free operation of the side-action unit.
With prior side-action cam mechanisms, both the cavity and core half of the mold need to be modified to accommodate the parts thereof. The cavity half requires a mounting bore for the previously described angled cam pin. In addition, there typically will be a pocket formed in the cavity half for a cam lock which provides the final lock for fitting when the mold halves are closed and prevents any blow-back of the side action mechanism due to molding pressure. The core half has a recess therein to accommodate the slide carrier and attaching the wear plates therein. Thus, the mold halves require substantial modifications and customizing to accept the numerous parts for the current side-action mechanisms. Accordingly, there is a need for a side-action mechanism which does not require as much customizing of the mold halves, and preferably which reduces or eliminates the present machining currently required of the cavity half for side-action mechanisms.
As the side-action mechanisms currently used in molds rely on parts that are fixed to the respective mold halves, there is no additional force besides that of the opening of the mold halves which pulls the side coring element from the mold cavity. In order to properly release the coring element from the surrounding plastic thereon, it is known to draft the coring pins so as to provide for better release characteristics from the cavity and the plastic that has shrunk around the pin in the cavity. The drafting facilitates removal by reducing the friction between the coring element and the plastic as it is being pulled from the mold cavity. Proper release of the coring element from the cavity is important so as to avoid damage to the molded part. Thus, a side-action mechanism which enhances the release of the coring element from the mold cavity when the mold is being opened would be desirable.
In prior side-action cam mechanisms, it is common for the angled pin to be withdrawn entirely from its corresponding carrier bore in the core half of the mold when the mold halves are opened. When this occurs, there is no positive hold on the slide carrier in the retracted position so as to keep the carrier bore properly aligned for subsequent insertion of the angled pin therein when the mold halves are closed. If the slide carrier is to move from this position and the mold halves are closed, it is likely that the angled pin and the mold itself can become damaged from such movement. Accordingly, it is known to provide detent retainers for side-action slide carriers attached in the core retaining plate of the mold--see U.S. Pat. Nos. 4,515,342; 4,768,747; and 5,397,226. However, these detent mechanisms do not provide a strong positive lock for the slide carrier so that the detents will release the slide carrier if a sufficient releasing force is present. The use of a detent mechanism also is an additional component of the side-action mechanism that must be manufactured and assembled into the mold, thus raising the expense and increasing the complexity associated therewith. Thus, a side-action mechanism which does not require a separate component for detenting and retaining the coring element withdrawn from the mold cavity would be desirable.